1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly to electrical enclosures for electrical switching apparatus, such as draw-out circuit breakers. The invention also relates to seal assemblies for electrical enclosures.
2. Background Information
Switchgear for electric power distribution systems includes electrical switching apparatus and their line and load terminations together with related equipment mounted in an electrical enclosure (typically a metal cabinet). Switchgear used in sections of electric power distribution systems operating at voltages up through 690 volts is classified as low voltage switchgear (according to international standards, although the ANSI standard for low voltage is a maximum of 600 volts). Typically, the electrical switching apparatus is a circuit breaker, but other switching apparatus such as, for example, network protectors, disconnect switches, and transfer switches are also mounted in such switchgear cabinets. Henceforth, the electrical switching apparatus will generally be referred to as circuit breakers, although it will be understood that other types of electrical switching apparatus can be used as well.
Typically, in such low voltage switchgear, multiple circuit breakers are mounted in each cabinet in cells stacked vertically in a forward compartment. The line and load conductors are mounted in rearward compartments and engage the circuit breakers through quick disconnects as the circuit breakers are installed in the cells.
Some electrical switching apparatus can be relatively large. In order to facilitate movement (e.g., installation; removal; maintenance), some circuit breakers are commonly coupled to draw-out mechanisms which permit such circuit breakers to be drawn out of the electrical enclosure. Accordingly, such circuit breakers are commonly known in the art as “draw-out” circuit breakers. Draw-out circuit breakers are described in further detail, for example, in commonly assigned U.S. Pat. No. 7,019,229, which is hereby incorporated herein by reference. See also U.S. Pat. Nos. 4,002,864; 4,002,865; 4,017,698; 4,728,757; 6,031,192; and 6,563,062.
The electrical enclosure for draw-out circuit breakers generally includes an outer structure having a top, bottom, rear and side walls, and a front access door or easily removable panel.
Circuit breakers are designed to trip in response to a trip condition (e.g., without limitation, an overcurrent condition; an overload condition; a relatively high level short circuit or fault condition). A high current fault interruption, for example, typically results in a substantial arc in the arc chamber of the circuit breaker. The arc forms rapidly expanding gases, and may generate flames and flying debris comprised of molten metal particles and fragments of various circuit breaker components.
Similar arcing can occur between adjacent conductors of different potentials, between an outboard line or load conductor and the switchgear cabinetry, and between the quick disconnects that are connected with the line and load conductors. Such arcing events are generally of greater magnitude and duration than those produced from fault interruption due to tripping of a circuit breaker. Such potential arcing events could result from a number of different scenarios such as, but not limited to: an operator leaving a tool in the switchgear prior to energizing the switchgear, an operator leaving a tool (or other object) on the back of a circuit breaker while racking the breaker onto a live bus, buildup of debris within the switchgear, animals entering the switchgear through venting holes and crossing a live bus, or some other type of unforeseen failure within the switchgear.
If the electrical enclosure is not sealed with respect to the circuit breaker, the arc gases and related debris can undesirably be expelled outwardly from the enclosure between the front access door and the circuit breaker, potentially causing injury to an operator or other person(s) adjacent the enclosure. Such arcing events are especially of concern during initial installation and racking of a circuit breaker by an operator.
One prior proposal for providing an arc resistant draw-out circuit breaker involves the use of a seal assembly including a seal between the circuit breaker and the electrical enclosure. However, known seal assemblies and/or seals therefor interfere with the ability to rack the circuit breaker in and out through the front access door.
There is, therefore, room for improvement in electrical switching apparatus, such as draw-out circuit breakers, and in electrical cabinet assemblies and seal assemblies therefor.